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The petrology of base metal sulfides and associated accessory minerals in rocks away from economically significant ore zones such as the Merensky Reef of the Bushveld Complex has previously received only scant attention, yet this information is critical in the evaluation of models for the formation of Bushveld-type platinum-group element (PGE) deposits. Trace sulfide minerals, primarily pyrite, pyrrhotite, pentlandite, and chalcopyrite are generally less than 100 microns in size, and occur as disseminated interstitial individual grains, as polyphase assemblages, and less commonly as inclusions in pyroxene, plagioclase, and olivine. Pyrite after pyrrhotite is commonly associated with low temperature greenschist alteration haloes around sulfide grains. Pyrrhotite hosted by Cr- and Ti-poor magnetite (Fe3O4) occurs in several samples from the Marginal to Lower Critical Zones below the platiniferous Merensky Reef. These grains occur with calcite that is in textural equilibrium with the igneous silicate minerals, occur with Cl-rich apatite, and are interpreted as resulting from high temperature sulfur loss during degassing of interstitial liquid. A quantitative model demonstrates how many of the first-order features of the Bushveld ore metal distribution could have developed by vapor refining of the crystal pile by chloride–carbonate-rich fluids during which sulfur and sulfide are continuously recycled, with sulfur moving from the interior of the crystal pile to the top during vapor degassing.

The potential for Nb, Ta, Li, Sn-mineralization as well as for precious stones for the Eastern Brazilian Pegmatite Province (EBPP) has been evaluated on the basis of 530 K-feldspar and 550 muscovite major and trace element analyses. The EBPP is situated mainly in the State of Minas Gerais, but encompasses also parts of the States of Bahia, Espírito Santo and Rio de Janeiro. The EBPP is the largest pegmatite province of South America. It was divided into the pegmatite districts of Itambé, Araçuaí, Safira, Nova Era, Aimorés and Espera Feliz. This was done to test whether the pegmatites of these districts differ in their mineralization potential and how geotectonic setting influences mineralization potential. The fractionation diagrams such as Cs, Zn, Li, Be, Ba versus K/Rb, Cs versus Ta/(Ta + Nb), and U, Na2O versus K/Cs for the pegmatite districts of Araçuaí and Safira show the widest range in fractionation. These pegmatite districts are leaders in the production of gem-quality tourmaline, aquamarine, morganite, and contain abundant spodumene, tantalite and columbite. In contrast, the Espera Feliz and Aimorés pegmatite districts are the most primitive districts examined and have a corresponding lack of rare-element mineralization. Literature data indicate that all studied pegmatites are of Brasiliano age, i.e., formed between 600 and 480 Ma. The pegmatites of Transamazonic age (1.9 Ga), found rarely in the study area, are of economic importance in the context of emerald mineralization, but seem to be of less importance for rare metal and other gemstone mineralization.

The Boliden deposit (8.3 Mt at 15.9 g/t Au) is interpreted to have been formed between ca. 1894 and 1891 Ma, based on two new U–Pb ID-TIMS ages: a maximum age of 1893.9 + 2.0/−1.9 Ma obtained from an altered quartz and feldspar porphyritic rhyolite in the deposit footwall in the volcanic Skellefte group and a minimum age of 1890.8 ± 1 Ma obtained from a felsic mass-flow deposit in the lowermost part of the volcano-sedimentary Vargfors group, which forms the stratigraphic hanging wall to the deposit. These ages are in agreement with the alteration and mineralization being formed at or near the sea floor in the volcanogenic massive sulfide environment. These two ages and the geologic relationships imply that: (1) volcanism and hydrothermal activity in the Skellefte group were initiated earlier than 1.89 Ga which was previously considered to be the onset of volcanism in the Skellefte group; (2) the volcano-sedimentary succession of the Vargfors group is perhaps as old as 1892 Ma in the eastern part of the Skellefte district; and (3) an early (synvolcanic) deformation event in the Skellefte group is evidenced by the unconformity between the ≤1893.9 + 2.0/−1.9 Ma Skellefte group upper volcanic rocks and the ≤1890.8 ± 1 Ma Vargfors sedimentary and volcanic rocks in the Boliden domain. Differential block tilting, uplift, and subsidence controlled by synvolcanic faults in an extensional environment is likely, perhaps explaining some hybrid VMS-epithermal characteristics shown by the VMS deposits of the district.

The Banded Hematite Jasper (BHJ) Formation of Noamundi region in Bihar, belonging to the lower part of the Iron Ore Group of early Precambrian age (c. 2900–3200 Ma), exhibits numerous primary depositional and diagenetic features, both in BHJ as well as the associated iron ore deposits. Observed primary depositional features include banding and bedding of different geometric-types, surface-markings including interference ripple-marks, current crescents, linear markings, scour-and-fill structures, etc. and within-mass microstructures such as spherulites, granules, discs and maculose cylindrical bodies. Diagenetic features, such as fabric changes, micro-dessication structures, gravity-density features, etc. and motion-and-disruption features of various kinds are also seen. The significance of various features in terms of probable mode and environments of deposition of BHJ and the iron ore beds has been considered. In general, shallow water environment of deposition in a region proximal to the shoreline with a rather steep paleoslope of the shelf has been surmised.

The Kenticha rare-element pegmatite, a globally important tantalite source in the Neoproterozoic Adola Belt of southern Ethiopia, is a highly fractionated, huge (2,000 m long and up to 100 m thick), subhorizontal, sheet-like body, discordantly emplaced in ultramafic host rock. It corresponds to the spodumene subtype of the rare-element pegmatite class and belongs to the lithium–cesium–tantalum petrogenetic family. The Kenticha pegmatite is asymmetrically zoned from bottom to top into granitic lower zone, spodumene-free intermediate zone, and spodumene-bearing upper zone. A monomineralic quartz unit is discontinuously developed within the upper zone. Whole-rock data indicate an internal geochemical differentiation of the pegmatite sheet proceeding from the lower zone (K/Rb ~36, K/Cs ~440, Al/Ga ~2,060, Nb/Ta ~2.6) to the upper zone (K/Rb ~19, K/Cs ~96, Al/Ga ~1,600, Nb/Ta ~0.7). The latter one is strongly enriched in Li2O (up to 3.21%), Rb (up to 4,570 ppm), Cs (up to 730 ppm), Ga (up to 71 ppm), and Ta (up to 554 ppm). Similar trends of increasing fractionation from lower zone to upper zone were obtained in muscovite (K/Rb 23–14, K/Cs 580–290, K/Tl 6,790–3,730, Fe/Mn 19–10, Nb/Ta 6.5–3.8) and columbite–tantalite (Mn/Mn + Fe 0.4–1, Ta/Ta + Nb 0.1–0.9). The bottom-to-top differentiation of the Kenticha pegmatite and the Ta mineralization in its upper part are principally attributed to upward in situ fractionation of a residual leucogranitic to pegmatitic melt, largely under closed system conditions. High MgO contents (up to 5.05%) in parts of the upper zone are the result of postmagmatic hydrothermal alteration and contamination by hanging wall serpentinite. U–Pb dating of Mn-tantalite from two zones of the Kenticha pegmatite gave ages of 530.2 ± 1.3 and 530.0 ± 2.3 Ma. Mn-tantalite from the Bupo pegmatite, situated 9 km north of Kenticha, gave an age of 529.2 ± 4.1 Ma, indicating coeval emplacement of the two pegmatites. The emplacement of the pegmatites is temporally related to postorogenic granite magmatism, producing slightly peraluminous, I-type plutons in the area surrounding the Kenticha pegmatite field. Fractionated members of this suite might be envisaged as potential parental magmas.

The ultramafic rocks of New Caledonia contain a diversity of disseminated ore minerals in non-economic amounts. Eighteen opaque minerals are described herein with pentlandite, millerite and heazelwoodite most prominent. Several new or unusual mineralogical features are recorded. These include an eutectic intergrowth between pentlandite and primary chalcocite, reaction between pentlandite and chalcocite to form chalcopyrite and millerite, exsolution intergrowth between pentlandite and millerite, between pentlandite and mackinawite and between millerite and cubanite. In the formation of the garnieritic ores of New Caledonia some of the nickel would appear to have been derived from the breakdown of disseminated sulphides as well as from the nickel inherent in the silicate minerals of the ultramafic rocks.